Dispersal and Seasonal Occurrence of Noctuidonema guyanense, an Ectoparasitic Nematode of Adult Fall Armyworm (Lepidoptera: Noctuidae), in the United States²

Migrant Spodoptera frugiperda (J. E. Smith) adult males were collected at 17 widely separated locations throughout the eastern half of the United States and were examined to determine if Noctuidonema guyanense Remillet and Silvain, an ectoparasitic nematode of adult Lepidoptera, were transported with the host. Nematodes were recovered from all locations where moths were captured. Nematode populations and parasitism of fall armyworm males were higher in the eastern states than in the Plains, Midwestern, and Central states (e.g., west Texas, Iowa, and Ohio). Percent parasitism and the number of nematodes per infested fall armyworm changed over time at each location. The initial immigrant fall armyworm males at a given location generally had few or no nematodes. These data suggest that moths with a moderate number of nematodes may be less able to disperse. Nematode populations peaked in mid-to-late August and then declined to a few or none by mid-October at locations north of the Gulf Coast area. Among other factors, temperature is apparently an important regulator of N. guyanense populations.